The present invention relates to a joint restraint for pipe fittings and particularly relates to an assembly useful for joining a fitting and a pipe enabling the transfer of thrust loads between the fitting and pipe.
In underground pipe systems, as well as other pipe systems, it is common to connect a pipe to a gasketed fitting. For example, T-fittings are generally connected at opposite ends to pipes and also to a lateral pipe. Other types of fittings include reducers where the fitting is used to reduce the flow diameter from one pipe to another. It will also be appreciated that there are thrust forces associated with the flowing of fluid in the pipes under pressure and that such thrust forces are typically reacted into the surrounding environment. Otherwise, the fittings will essentially be forced off the end of the pipe, i.e., the fitting will blow off of the pipe. Gasketed joints often do not transfer such structural loadings. Joint restraints, however, are typically used on pipe joints and are specifically designed to resist the thrust force at the fitting.
Two such joint restraint systems are disclosed in U.S. Pat. Nos. 4,336,959 and 4,009,036. In the first mentioned patent, a bell at the end of one pipe receives an end of the other pipe. The other pipe includes semi-circular elements secured for example by serrations to such other pipe with bolts extending axially between the joined elements and a retainer ring secured behind the bell of the first pipe. The second patent discloses a plurality of bolts to secure an annular body to an end of one pipe received in a flanged end of another pipe. The flanged end and the annular body are secured to one another by axially extending bolts. In both of these patents a significant number of parts are utilized and which require assembly on site. These parts are also arranged about the joint in a manner obscuring certain of the couplings between the pipes. For example, inspection of the pipes lying in a trench to insure proper coupling therebetween using these joint systems is virtually impossible. There is thus developed a need for a joint restraint which utilizes relatively few parts, is easy to assemble and can be readily visually inspected to insure a proper coupling.
In accordance with the preferred aspect of the present invention, there is provided a joint restraint for coupling a pipe and a fitting wherein loadings, e.g., axial thrust forces, are transferred between the fitting and the pipe reducing any need for thrust blocks or other mechanisms at the installation site for reacting the thrust loads into the surrounding environment. The joint restraint includes a shell having a pair of arms for engaging behind lateral lugs projecting from the fitting. The shell also includes a lateral opening for receiving the radially projecting flanges of a clamp ring received within the interior of the shell. With the pipe inserted through the shell and clamp ring and into the open end of the fitting, the lateral arms on the shell engage behind the lugs on the fitting. By closing the ring about the pipe and thereby securing the pipe and ring against axial movement relative to one another, the ring serves as a stop for the shell precluding axial movement of the fitting from the pipe. The engagement of the shell arms and the lugs on the fitting preclude axial movement of the pipe from the fitting. Thus, the pipe and the fitting are restrained from axial movement relative to one another by transfer of loads from one to the other through the shell and clamp ring. It will be appreciated that the joint restraint is compact and may be handled as a single unit requiring only one actuation, i.e. turning a bolt, to secure the clamp ring to the pipe. Problems associated with asymmetrical loading of the pipe and fitting connections are avoided notwithstanding the use of a single bolt to secure the clamp ring to the pipe. Also, the joint restraint is modular as it can be used on any compatible existing fitting, is inexpensive to manufacture and is low in cost in comparison with prior joint restraints.